I think it depends on the names. For example, CatherineCollins sounds good. So does Amy Applegate. But BrianBrown, not so much. I think what matters for me is the consonants and how hard they are. Violet "Hickory-with-a-V" sounds a little too V heavy for my personal taste. But I don't think its sounds childish, it just has a little too much of the same sound. VioletElaine "Hickory-with-a-V" sounds very professional and I don't think having an alliterative name would stop her from doing great things in the world. So, it would not be the end of the world, but I have a slight dislike for this full name alliteration.

I think alliteration depends on the specific combination. FranFrey, for example, isn't the best combination, but JenniferJones is just fine.

When I first heard it, I wasn't thrilled by Violet V-ckory, but hearing it as a doctor or lawyer in the examples merrybells listed, I changed my mind. I like it, but it sounds a little bit like a fictional character, maybe a Roald Dahl one.